Well the easist way would be to install a server Os on one then cart it next door and use dial up networking
Seriously I assume that you wish to network these machines using the existing phone line in your home. You can get special ethernet cards that can do this. One example of such would be linksys kit. Here's the link:
http://www.linksys.com/products/product.asp?prid=130&grid=3
These work at 10 MPS and as a bonus you can still use your cable modem to connect to the net and surf on both machines.
Ps On my home network I only have 56K modems. Sharing this between 3 machines is not a good idea!